The objectives of this research are to provide general information on the process of enzymatic hydroxylation and, more specifically, on the characteristics of phenylalanine hydroxylase and its pteridine cofactor. Recently, the phenylalanine hydroxylase from Pseudomonas sp. has been partially purified and its mechanisms of activation and action investigated. It has been shown to be a small, pteridine-requiring hydroxylase with a stringent iron requirement. Current efforts are directed toward: (1) purifying the enzyme to homogeneity via affinity chromatography on pteridine-agarose; (2) investigating the state of the iron in the molecule; (3) preparing and characterizing antibody to the enzyme; (4) isolating the mRNA for the enzyme.